It is a scholarly citation database, an attempt to provide free citations to scholarly publications that are typically "fee-based". It began in 2004 and is still in a Beta version, so be aware that things keep changing with the database.
Google Scholar's database indexes items Google considers "scholarly," including articles, theses, books, preprints, abstracts, conference proceedings, and technical reports. Some, but not all, articles found in Google Scholar will be accessible at MIT.
A nice feature of Google Scholar is that it can link to full text articles in MIT Libraries' electronic collections. To activate this function on your computer, go to Google Scholar and click on Scholar Preferences. Type MIT Libraries into the Library Links box. Click on Save Preferences.
It is difficult to determine how much of the scholarly literature is included in the database, but only a portion of the literature of any discipline is indexed in Google Scholar.
Great for getting started in an area, Google Scholar is a useful tool when used in conjunction with the specialized resources available through the MIT Libraries. You should also use Barton, the MIT Libraries catalog as well as subject-specific databases included in Vera to be most comprehensive with your research.